1. Field of the Invention
The present invention relates to an ultrasonic transducer that transmits or receives ultrasonic waves by driving a piezoelectric body.
2. Description of the Related Art
Some of the known ultrasonic transducers have configurations in which a piezoelectric body is disposed in a case.
FIG. 1A is a sectional view of a known ultrasonic transducer.
The ultrasonic transducer 100 includes a case 101, a piezoelectric body 102, a sound-absorbing member 103, a filler 104, and lead wires 105. The piezoelectric body 102 is bonded to the inner surface of the top of the case 101 with an adhesive (not shown). The case 101 has a cylindrical shape with a closed end. The filler 104 fills the space within the cylinder of the case 101 and is fixed therein to close the case 101. The sound-absorbing member 103 is disposed in the space within the case 101. One of the lead wires 105 is connected to the piezoelectric body 102, and extends out of the case through the filler 104.
This structure causes multiple reflections of sound waves in the inner space of the case 101. Sound waves attenuate with the multiple reflections. However, if sound waves reverberate for a long period of time, the waveform of the transmitted waves of the ultrasonic transducer may become dull due to the reverberation, or received waves may be obscured by the reverberation. Accordingly, the ultrasonic transducer 100 is provided with the sound-absorbing member 103 within the case 101 so as to absorb sound waves emitted from the piezoelectric body 102 toward the open side of the case 101 and, thus, to reduce the effects of reverberation.
Another type of the known ultrasonic transducers uses metal pins instead of the lead wires, as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2007-318742.
FIG. 1B is a sectional view of another known ultrasonic transducer.
The ultrasonic transducer 200 includes a case 201, a piezoelectric body 202, a fixing plate 203, a filler 204, and metal pins 205 arranged to transmit electrical signals to the outside. This type of ultrasonic transducer 200 uses metal pins 205, instead of lead wires, and includes a resin fixing plate 203 arranged to fix the metal pins 205.
With this structure, the fixing plate 203 is spaced a predetermined distance from the inner surface of the top of the cylindrical case 201 having a closed end, and to which a spring metal terminal 206 is secured to electrically connect one of the metal pins to the piezoelectric body 202. If the spring metal terminal 206 resonates with the piezoelectric body 202, the ultrasonic transducer 200 is likely to be adversely effected by reverberation. Accordingly, the resonant frequency of the spring metal terminal 206 is set to a frequency such that the spring terminal 206 does not resonate with the piezoelectric body 202. Thus, the effects of reverberation on the ultrasonic transducer 200 are reduced.
The effects of reverberation on the ultrasonic transducer can be reduced by providing a sound-absorbing member within the case, or by appropriately setting the resonant frequency of the spring metal terminal, as described above. However, theses countermeasures cannot completely eliminate reverberation of ultrasonic waves. Thus, there is a need to further reduce or eliminate the effects of reverberation.